During production, substrates are often handled by robotic arms that are equipped with specialized tools, or “end effectors,” that are adapted for lifting and moving the substrates between a substrate cassette or other container and a processing platen located within a process chamber. End effectors typically engage the substrates from below. As such, while an end effector can pick a substrate directly from a cassette, it typically cannot directly deposit a substrate onto the surface of the platen.
Thus, the platen often includes a set of movable pins that protrude upward through openings in the top surface of the platen. The end effector positions the substrate above the pins, the pins move upward to pick up the substrate and raise it above the end effector. Once the pins raise the substrate out of engagement with the end effector, there is sufficient distance between the substrate and the platen top surface to allow the end effector to retract from the platen. The pins can then be retracted through the openings, lowering the substrate onto the platen.
An electrostatic chuck can then be used to secure the substrate to the platen so that one or more processing steps can be performed. When processing is complete, the electrostatic chuck can release the substrate, the pins are moved upward to protrude through the openings and lift the substrate above the platen so the end effector can engage and remove the substrate from the process chamber.
As will be appreciated, problems such as substrate breakage, substrate mis-positioning, substrate sticking, and the like, can occur before, during or after the substrate transfer and/or processing operations. It would be desirable, therefore, to provide a system capable of detecting such problems so that corrective action can be taken in an efficient and cost effective manner.